This invention relates to a device and a method for the physiological frequency control of a heart pacemaker equipped with a stimulating electrode by means of a control unit as well as to a method for operating such a device.
The most common applications of pacemaker therapy are the permanent and the temporary electrostimulation of the heart. On occassion, a combination of both methods may be necessary in cases which cannot be judged unequivocally. Permanent electrostimulation of the heart is used if Adams-Strokes attacks occur or in the event of total AV block (AV=atrioventricular node). In cases of bradycardic heart arrhythmia, temporary electrostimulation of the heart must be provided so that the physical capacity of the patient is improved.
For the permanent electrostimulation of the heart, heart pacemakers are known which contain a fixed frequency generator which delivers, for instance, 70 current pulses per minute at a constant rate. These heart pacemakers are of simple design and have a long service life even with standard chemical batteries. Such heart pacemakers can be used particularly for older people for whom a heart time-volume on the basis of 70 beats per minute is sufficient for their still tolerable extent of physical stress. In addition, the rhythm of the patient's heart itself is suppressed at least approximately. If spontaneous actions by the patient occur from one or several automation centers, the parasystolic behavior can lead not only to an irregular beat sequence with bunched occurrence of disturbed pacemaker pulses; it also can trigger, in particular, tachycardic states all the way to chamber fibrillation if the artificial stimuli fall into the valnerable phase, i.e., the T-wave of the intrinsic preceding action.
In addition, different types of so-called demand pacemakers are known. In demand sets, the pulse of the heart pacemaker is inhibited via an electrode located in the ventricle by the potential of the R-spike of the intrinsic actions as long as its frequency is above, for instance, 70 beats per minute. If it drops below this value, the device is switched on automatically and takes over the stimulation. In the "stand-by-pacer," the R-spike of the intrinsic rhythm acts, via the electrode, as a trigger pulse, to which the pacemaker is subordinated in the frequency range, for instance, of between 70 and 150 beats per minute with matched signal lapse. If intrinsic pulses are missing or if the R-spike spacings are smaller than between 300 and 400 msec, artificial stimulation is applied. If, however, the latter exceeds an upper predetermined pulse per minute value of, for instance, 150, the heart pacemaker cuts the frequency in half, i.e., it takes over the electrical stimulation of the heart with a correspondingly reduced pulse delivery. With these two types of demand pacemakers, the parasystolic state is avoided and an orderly side by side arrangement of the internal rhythm and artifical stimulation is obtained.
Furthermore, an electrochemical device for determining the oxygen content of a liquid is known. The measuring cell of this device consists of a tubular body in which a cathode and an anode are arranged in an electrolyte. The one end face of the measuring cell is provided with a diaphragm which is fastened by a sealing ring and a cap provided with an opening. This diaphragm separates the liquid to be examined from the electrode arrangement. The measurement principle consists of the electrochemical reduction of oxygen (O.sub.2) where an oxygen diffusion limiting current is brought about at the electrode through the diaphragm. Thereby a measuring signal proportional to the concentration if obtained (U.S. Pat. No. 2,913,386). With a measuring cell of such a design, the oxygen concentration in the blood or tissue can be measured in vivo, however, only for a short time, for instance, for several days since the measuring cell becomes surrounded by developing connective tissue layers, and the measuring signal is thereby falsified.
It is, thus, an object of the present invention to describe a heart pacemaker which makes possible a mode of operation which is adapted to the physiology, is simple and trouble-free.